The above question has fostered considerable discussion in the global warming debate in recent years. Responses range across a spectrum of viewpoints; at one end current climate change is viewed as entirely natural, while at the other it is considered wholly human-caused. One of the more recent research teams to investigate this topic was that of Babich et al. (2017), who published their work in the scientific journal Doklady Earth Sciences.

Writing as background for their study, the four Russian scientists note that “it is very important to find patterns in climate variations in order to build a reliable forecast of future climatic changes.” Thus, it was their objective to “attempt to detect some patterns common to the extratropical part of the Northern Hemisphere in climate evolution over the past few millennia that could serve as the basis for long-term predictive climate patterns.”

To accomplish their work, Babich et al. performed three forms of spectral decomposition (Hilbert-Huang transformation, wavelet transform and Fourier transform) on five paleoclimate reconstructions with records extending approximately 2000-4000 back in time. Three of the records were more concentrated in the regions of central Asia, China and northeastern Europe, while the other two were “more generalized and have hemispheric scale.” The underlying data from which the climate reconstructions were created came from a wide variety of sources, including “lacustrine, fluvial, and marine sediments; pollen, dendrochronology, and speleothem data; ice cores and historical facts, etc,” and the reconstructions were considered by the authors to contain “quite reliable information for detection of sufficiently long-period climatic variations.”

So what did the spectral analysis methods reveal about the climate data? In the words of the authors, they revealed “the presence of low- and mid-frequency variations in them, which have a quasi-periodic character.” More specifically, they discovered the presence of climate cycles with established periodicities of approximately 1000, 500, 350 and 200 years.

In commenting on their findings, Babich et al. say that the ~1000 and 200 year periodicities “are most clearly manifested and are global,” adding that previous authors have linked these oscillations to changes in solar insolation. Consequently, in light of these several findings, the researchers conclude that “there is every reason to believe that the revealed quasi-periodic components in the climate variability of the extratropical zone of the Northern Hemisphere are natural, conditioned by natural cyclical phenomena and can serve as a basis for long-term predictive climatic constructions,” which does not leave a lot of room for human-induced climate change in explaining past, current or future climate.

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